Centrifugal thickener

ABSTRACT

A slurry thickener in which are employed both centrifugal force and an axial pressing force. The latter is made possible by the special conical configuration of the end portions of an otherwise cylindrical thickening cylinder.

s21 U.S. Cl.

United States Patent [72] Inventors Alt'Torsten Okvist Skarblacka;

Nils Olof Nilsmar, Kallhall, Sweden [21] AppLNo. 772,253

[22] Filed Oct. 31,1968 [45] Patented Feb. 16, 1971 [73] Assignee MaskinAB N.A. Eie [32] Priority Nov. 2, 1967 [33] Sweden [31] 15,033/67 [54]CENTRIFUGAL THICKENER 5 Claims, 3 Drawing Figs.

[51] Int. Cl B0411 3/02 [50] Field of Search 210/376 [56] ReferencesCited UNITED STATES PATENTS 1,944,391 1/1934 Altpeter 210/376 PrimaryExaminer-J. L. DeCesare Attorney-Pierce, Scheffler & Parker ABSTRACT: Aslurry thickener in which are employed both centrifugal force and anaxial pressing force. The latter is made possible by the special conicalconfiguration of the end portions of an otherwise cylindrical thickeningcylinder.

Patented Feb. 16, 1971 3,563,387

' Sheets-Sheet 1 v Fig.7

3 Sheets-Sheet 2 Patentd Feb. 15,1911

Patented Feb. 16, 1971 3 Sheets-Sheet 5 CENTRIFUGAL THICKENER Thisinvention relates to thickening means for slurries of dif ferent typesand particularly is concerned with the provision of a continuousthickener operating by assistance of centrifugal force and an axialpressing force.

In similar conventional thickeners the thickening is effected only bycentrifugal force, while according to the present invention bothcentrifugal forceand a special axial pressing force are applied to thematerial to be thickened. Hereby it is possible to employ a means whichis considerably simpler than heretofore, and at the same time toincrease the throughput of the apparatus as well as the dry content ofthe product.

The centrifugal thickener according to the present invention comprises amachine housing, which includes a rotor, a rotor shaft and rigidlyconnected with said rotor, a perforated thickening cylinder feed meansand discharge means in the cylinder the feed means being apipeprojecting inwardly through one end of the rotor shaft, and thedischarge means being a plate which is adapted to rotate with thethickening cylinder and is axially movable in relation to the same.

The present invention is characterized in that the thickening cylinderis provided with end cones inclined conically inwardly, the ends ofwhich cones' 'are mounted within the cylinder and form a radial inwardlyprojecting edge, said cones being designed in two steps, viz. an innerstep located closest to the cylinder and an outer, more remote step,said inner step having a mean diameter smaller than that of the stepwhich is located outside thereof.

The invention will be described in greater detail in the following, andwith reference to the accompanying drawing in which:

FIG. 1 shows a longitudinal section through a thickener according to theinvention;

FIG. 2 shows in a schematic way a longitudinal section through one endof the thickening cylinder, the discharge plate in position to pressslurry against the end; and

FIG. 3 shows in a schematic way a longitudinal section through. thelower half of a two-step centrifugal thickener according to theinvention.

As appears from the drawing, the thickener according to a preferredembodiment comprises a machine stand with upwardly extending bearingbrackets 2 which support a machine housing 3 and a rotor 4 mountedrotatably therein. Said rotor 4 has a relatively heavy tubular throughshaft 5 with tubular shaft journals 8 and 9 at each end, said journalsprojecting outwardly each through the adjacentend wall of the machinehousing 3 and being supported in the bearing brackets 2.

Within the rotor 4 and rigidly connected therewith there is mounted athickening cylinder 31 with perforated wall. Said cylinder 31 issubstantially straight, but it has end cones 32 inclined to the axis.The conicity, however, is small, for example approx. 12.

The end cones 32 are inserted into the thickening cylinder 31 proper insuch a manner that the inner end of each cone forms a radially outwardlyprojecting edge 41, which is intended to prevent the watery slurryor'liquid to be pressed up in the end cones. Experience has shown thatin thickness of the centrifugal type the tendency is for the liquid tocontinue to flow upwards closest to the cone wall and over its edge,thereby taking along already thickened slurry, while the alreadythickened slurry built up thereupon is discharged to a considerablyreduced extent, at the same time as the moisture content of the slurryexceeds the desired value. It has also been found that the thickenedslurry in the end cones at times tends to slide on the lowermost waterylayer downwards (i.e., back) into the thickening cylinder.

For counteracting this tendency of the slurry to slide back, accordingto a further characterizing feature of the present invention we provideeach of the end .cones with a shoulder or [which is located outside ofsaid step, whereby the return motion of the slurry is stopped.

Approximately in the middle between the ends of the thickening cylinderthe rotor shaft 5 is provided with a number of openings 33 through whichmaterial to be thickened is fed into the cylinder 31. The material isintroduced through one of the tubular shaft journals 8 of the rotor 4.At the inner end of said journal there are mounted shovel-shapeddischarge elements 34 for improving the radial distribution of thematerial when being fed into the cylinder. The material is fed axiallyalong the inner periphery of the thickening cylinder and dischargedthrough one or the other of its ends, by means of a reciprocatingdischarger in the form of an annular disc 35 extending radially betweenthe rotor shaft 5 and the inner periphery of the thickening cylinder 31.At some distance from the outer edge of said disc ports 37 are provideduniformly distributed about the disc 35.

The discharge disc 35 is rigidly connected with a dampershaped bushing38 mounted slidably on the rotor shaft 5 and guided axially by a controlrod 21 projecting inwardly through the second tubular shaft journal 9 ofthe rotor 5 via a guide pin 39 shown in a cross section and extendingupwards through a longitudinal slot 40 in the rotor shaft 5.

The thickener according to the present invention operates as follows.Material to be thickened, hereinafter called slurry, is fed in throughthe left-hand tubular shaft journal 8 to approximately the middle of thethickening cylinder 31 where the rotor shaft 5 is provided withperipheral openings 33 through which the slurry is fed centrifugallyinto the rotating thickening cylinder by assistance of the shovel-shapedfeed elements 34. The discharge disc 35 is reciprocated between the endsof the cylinder 31 and, by scraping, takes along the slurry which hasbeen fed in, which slurry on its travel to the end of the cylinder ispressed against the perforated cylinder wall by the centrifugal forceand thereby partly thickened. The water pressed out falls down into anoutflow funnel 26 and is discharged, while the slurry in its thenrelatively thickened state is advanced further to the end of thethickening cylinder where the slurry must :move upwards on the inclinedplane formed by the conically inwardly inclined end extensions of thecylinder. The motion of the slurry is thereby braked, and the pressurefrom the discharge disc 35, which continues its motion, increases andthereby presses additional water out of the slurry. During the pressingoperation against the end a dam of relatively dry slurry is built upahead of the discharge disc and contributes to improving the pressingeffect of the disc against the slurry. The watery slurry and the liquidwill place themselves at the inner surface, radially seen, and can flowback through ports 37 in the discharge disc for being again thickened inthe cylinder, while part of the more thickened slurry is fed out at eachstroke of the discharge disc through the end of the cylinder and fallsdown into a discharge shaft 27 and transported away.

The present invention has rendered possible a substantially simpler andthereby less expensive thickening means. Owing to the double thickeningaction the capacity of the thickener is increased and at the sametimeits effectiveness is improved, which results in a dryer slurry.

FIG. 3 shows a modification of the thickener according to FIGS. 1 and 2for thickening in two steps.

The thickening cylinder 44 is divided by two locking rings 45 into aninner thickening zone in the middle and two outer thickening zoneslocated between the locking rings and the end cones. The discharge plate46 moves only within the inner thickening zone and is connected byaxially extending rods 47 with two outer discharge members 48 adapted tobe moved each in its zone of the outer thickening zones.

The locking rings 45 have a substantially triangular cross section, witha point 49 being directed to the inner thickening zone and a radial edge50 being directed to the outer thickening zones. Thus, when thedischarge plate 46 feeds slurry against one of the locking rings 45, theslurry is pressed upwards on the inclined side of the ring, whereby theuppermost watery slurry layer flows back to the inner thickening zonefor again being thickened, while the dryer slurry at every stroke of thedischarge plate is fed over the locking rings into the outer thickeningzones where it is subjected to additional thickening. The outerdischarge members are rings 48 with a triangular cross section havingone point and one inclined side facing towards the locking rings, whilean edge perpendicular to the wall of the thickening cylinder facestowards the end cones.

When one of the outer discharge rings 48 moves against one of thelocking rings 45, the slurry in this thickening zone will be movedagainst the locking ring and thereby be fed upwards on the inclined sideof the discharge ring 48 and be pressed by the locking ring 45 over theedge of the discharge ring down into the outer thickening zone. Alreadyat this first pressing motion a certain thickening is effected. When thedischarge ring 48 thereafter moves against its end cone 32, continuousthickening is effected, because the centrifugal force all the time actsupon the slurry. When the slurry thus thickened is pressed upward on theend cone, a certain additional thickening takes place at the same timeas the watery slurry flows back to the thickening zone.

In conventional centrifugal thickening apparatus the thickened slurrymust be dried or pressed subsequent to the thickening for arriving at asufficiently low-moisture content to permit the slurry to be burnt.

By utilizing the centrifugal thickener according to the presentinvention, however, no extra thickening by pressing is required, becausethe slurry already in the centrifugal thickener is given a dry contentof up to 40 percent, which is sufficient for allowing direct burning.

We claim:

1. in a horizontal, centrifugal thickener for pulp and other slurries,comprising a machine housing including a shaft-supported rotor with anopen, perforated thickening cylinder, a feed means substantiallycomprising a pipe projecting inwardly through the rotor shaft, and adischarge means adapted to rotate with and to be moved axially inrelation to the thickening cylinder, the end portions of said openthickening cylinder being provided with slightly inwardly inclined endcones, the improved construction according to which the cone ends form alow radial edge, and in which each of the end cones of the thickeningcylinder includes two steps, the step located closest to the cylinderhaving a means diameter smaller than that of the step located outsidethereof, and said discharge means comprising a plate provided with aplurality of axially extending ports spaced inwardly from the peripherythereof for allowing return flow of watery slurry.

2. Centrifugal thickener according to claim 1, in which the feed meanscomprises a feed pipe which is provided at its end with shovellikedistribution members for throwing material, fed in centrifugally, outinto the thickening cylinder through suitable openings in the rotorshaft.

3. Centrifugal thickener according to claim 1, in which the dischargemeans comprises a disc which is operated axially by assistance of acontrol rod projecting inwardly through the rotor shaft directly infront of the feed pipe, the disc being connected with said control rodbyv a guide pin extending through a longitudinal slot in the rotorshaft.

4. Centrifugal thickener according to claim 1 for thickening in twosteps, in which the thickening cylinder comprises a first innerthickening zone defined by l two locking rings having substantiallytriangular cross section, and (2) two outer thickening zones locatedbetween the locking rings and the end cones adjacent thereto, and inwhich said discharge means includes a plate which moves only within theinner zone and is connected by axially extending rods with a dischargemember in each of the outer thickening zones.

5. Centrifugal thickener according to claim 4, in which each of theouter thickening zones comprises a ring, having substantially triangularcross section, of which ring one point faces towards the innerthickening zone and a radial edge faces towards the end cone.

1. In a horizontal, centrifugal thickener for pulp and other slurries,comprising a machine housing including a shaftsupported rotor with anopen, perforated thickening cylinder, a feed means substantiallycomprising a pipe projecting inwardly through the rotor shaft, and adischarge means adapted to rotate with and to be moved axially inrelation to the thickening cylinder, the end portions of said openthickening cylinder being provided with slightly inwardly inclined endcones, the improved construction according to which the cone ends form alow radial edge, and in which each of the end cones of the thickeningcylinder includes two steps, the step located closest to the cylinderhaving a means diameter smaller than that of the step located outsidethereof, and said discharge means comprising a plate provided with aplurality of axially extending ports spaced inwardly from the peripherythereof for allowing return flow of watery slurry.
 2. Centrifugalthickener according to claim 1, in which the feed means comprises a feedpipe which is provided at its end with shovellike distribution membersfor throwing material, fed in centrifugally, out into the thickeningcylinder through suitable openings in the rotor shaft.
 3. Centrifugalthickener according to Claim 1, in which the discharge means comprises adisc which is operated axially by assistance of a control rod projectinginwardly through the rotor shaft directly in front of the feed pipe, thedisc being connected with said control rod by a guide pin extendingthrough a longitudinal slot in the rotor shaft.
 4. Centrifugal thickeneraccording to claim 1 for thickening in two steps, in which thethickening cylinder comprises a first inner thickening zone defined by(1) two locking rings having substantially triangular cross section, and(2) two outer thickening zones located between the locking rings and theend cones adjacent thereto, and in which said discharge means includes aplate which moves only within the inner zone and is connected by axiallyextending rods with a discharge member in each of the outer thickeningzones.
 5. Centrifugal thickener according to claim 4, in which each ofthe outer thickening zones comprises a ring, having substantiallytriangular cross section, of which ring one point faces towards theinner thickening zone and a radial edge faces towards the end cone.